Method and apparatus for vehicle traffic control

ABSTRACT

A method for vehicle traffic control is provided which is basically adapted to aircraft and includes a method for aircraft control to eliminate hazardous operating conditions, a method for determining a potential conflict between two or more aircraft in sufficient time to effect correction, a method for determining an effective maneuver to avoid collision, a method for predicting control sector overload, a method for predicting terminal overload, and as a result of conflict, determination of an alternate flight plan or necessary time delay in takeoff to minimize flight costs. The means to accomplish these methods is a sophisticated data processing system properly programmed to a previously prepared algorithm. Preferably, the invention contemplates use of an associative processor so that all calculations can be performed on each aircraft or vehicle simultaneously in parallel. The invention also contemplates a satellite position measuring system to determine conflict of aircraft or surface vehicles over large water expanses. In addition, the system contemplates determining if a given flight path may intersect hazardous weather, or that an aircraft has safe minimum terrain clearance as the system can provide command instructions or controls in accordance with the system information generation.

United States Patent Meilander 51 June 6,1972

[54] METHOD AND APPARATUS FOR VEHICLE TRAFFIC CONTROL Willard C.Meilander, Kent, Ohio [72] Inventor:

[73] Assignee:

[52] US. Cl. ..235/l50.23, 343/5 DP, 343/112 C,

s l 1 m. C]. .cner 15/48 [58] Fieldoi'Search ..343/5 DP,7ED, 112C,IIZCA; 235/l50.23, 150.24

OTHER PUBLICATIONS Eddey, E. E. The Use of Associative Processors inRadar Tracking and Coorelation, Proceedings of the National AerospaceElectronics Conference, 1967 BEACON DATA LINK Primary Examiner-Eugene G.Botz Assistant ExaminerR. Stephen Dildine, Jr. Attorney-J. G. Pere andL. A. Germain ABSTRACT A method for vehicle traffic control is providedwhich is basically adapted to aircraft and includes a method foraircraft control to eliminate hazardous operating conditions, a methodfor determining a potential conflict between two or more aircraft insufficient time to effect correction, a method for determining aneffective maneuver to avoid collision, a

a method for predicting control sector overload, a method for predictingterminal overload, and as a result of conflict, determination of analternate flight plan or necessary time delay in takeoff to minimizeflight costs. The means to accomplish these methods is a sophisticateddata processing system properly programmed to a previously preparedalgorithm. Preferably, the invention contemplates use of an associativeprocessor so that all calculations can be performed on each aircraft orvehicle simultaneously in parallel. The invention also contemplates asatellite position measuring system to determine conflict of aircraft orsurface vehicles over large water expanses. In addition, the systemcontemplates determining if a given flight path may intersect hazardousweather, or that an aircraft has safe minimum terrain clearance as thesystem can provide command instructions or controls in accordance withthe system information generation.

17 Claims, 14 Drawing Figures men spar-:0 VEHICLE We AIR CONTROL 22POSITION ACQUISITION W ASSOCIATIVE |SPLA SYSTEM PROCESSOR AIR TRAFFICCONTROL COMMUNICATIONS PATENIEDJuu 5 I972 3, 6 6 8 .403

SHEET 10F 9 BEACON DATA LINK HIGH SPEED VEHICLE TARGET AIR CONTROLPOSITION ACQUISITION g ASSOCIATIVE SYSTEM PROCESSOR ELQLJ Am TRAFFICCONTROL COMMUNICATIONS 7 192? RADAR PULSETO-PULSE ,{coNvERs|oN TOPREDETERMINED} CORRELATION :SYSTEM COORDINATES TRUE SCAN-TO-SCAN ISMOOTH AND CLUTTER g c ,A|RCRAFT p CORRELATlON REDICT REJECT DECLARETARGETS 104 I06) I08 HO) TRUE TARGETS TRUE TARGETS GROUND CLUTTER ANDGROUND CLUTTER NOISE ---TRACK-WH|LE-SCAN (TWS) PROCESS :I

INVENTOR WILLARD C. MEILANDER MAW W ATTORNEYS FOR CORRELATED TARGET0.5;; SEC.

PATENTEDJIIII 6l972 3668, 103

SHEET 30F 9 I20 F| G- 4 RADAR I22 ouANTIzER I28 I30 f v '24 TIME RANGECOMPARAND REFERENCE COUNTER REG STER AZIMUTH E AZIMUTH E ENCODER COUNTERAP TARGET RANGE AZIMUTH HITS BUSY BIT UPDATE ACQUIRE l l3 ans 5 BITS 4ans l BIT I BIT I BIT I a I l ACQUIRE II IB'T TOTAL mm 26 sTART WAIT FORTARGET DECLARATION FROM SEARCH FOR RADAR EMPTY WORD 0.8;, Sec.

V BETWEEN LIMITS WRITE NEW MATCH FOUND SEARCH ON RANGE TARGET 2.6 Sec.0.5 See. 1' YES P POST UPDATE BIT WILLARD C. MEILANDER ATTORNEYSPATENTEDJIIII SL972 3,668,403

SHEET U 0F 9 WAIT FOR END OF SEARCH ON READ OUT RADAR PULSE ACQuIREISELECTED REPETITIoN PERIOD AND H|TS=8 TARGETS 0.5}! Sec. k 2.0 18ec.SEARCH 'ON UPDATE AND ACQUIRE I BITS Q2 5 SEARCH ADD AZ TO I PSUCCESSFUL? AZIMUTTH OF ADD I T0 2 HITS SELECTED 0F SELECTED TARGETSTARGETS 2;: Sec. O.4 .ISec. SET: ACQUIRE II V V r 3 BIT II=I SEARCH ON 5E HITS=C 9 AzIIvIuTI-I AZT- m z 2 0.5pSec. AND HITS [a 4 I SEARCH ON ANDACQuIRE I ACQUIRE ll 0 5 AND NoT P UPDATED 0.2}ISEC.

SEARCH SUCCESSFUL? ADD I To Z: HITS OF SELECTED TARGETS ZySec.

DELETE TARGETS SEARCH ON .5 i 0 ACouIRE ll AND H|TS=8 CHANGE SEARCH0.5}ISSC. CRITERIA INVENTOR WILLAR FIG-7 D C. MEILANDER fllwdQz/wATTORNEYS PATENIEIJIIII 6 I972 3,668,403

SHEET 5 BF 9 l G 8 UNCORRELATED -4---STATE l REPORT RECEIVED E PUT V-MlBOX AROUND LATEST No NEw REPORT REPORT IN BOX NEw REPoRT IN BOX SMOOTHAND PREDICT PUT w=MI BOX +-sTATI-: 2 AROUND r PREDIcTED N0 NEW POSITIONREPORT IN BOX {NEW REPORT IN BOXISMOOTH AND PREDICT PUT x-MI BOX 3AROUND PREDICTED No NEw POSITION REPoRT IN Box NEw REPoRT IN BOXISMOOTHAND PREDIcT PUT x-MI BOX AROUND PREDICTED NO NEw O O NEW REPORT IN aox:REPORT SMOOTH AND PREDICT IN BOX Y NEW REPoRT m.

PUT Y-Ml BOX PUT z MI BOX AROUND AROUND PREDICTED PREDICTED No NEWPOSITION POSITION STATE 7 REPORT A sTATE 6 STATE 5 ONEW REPORT Box Box:SMOOTH PUT Z-MI Box AND PREDIcT AROUND E PREDICTED NO NEW REPORTPOSITION IN BOX Y= 0. x +b Y= d x b INvENToR WILLARD C. MEILANDERIQMMQMM ATTORNEYS PATENTEDJIIII 5 I972 3, 668,403

SHEET 7 [IF 9 CORRELATE P WITH TRACK T SELECT TRACK T cALcu ATE a A xTANY FLAG ans [Fr SET T bT XT dTYT ISPTI J MIN MANEUOVER DECISIONCRITERIA IF 0 sET, cALcuLATE TIME FOR ALL OTHER (1 TRACKS T0 COLLIDECALCULATE T WITH I?A=CTXCIT XI/XI] Y- a T' YT GTXT a i= XI' O'IYI n EXITv bi=Y (1;X SET FLAG YES E I' 'r] BITS=| CALCULATE xcoLusloN T" i i d-GT FOR FLAG BIT S 0 CALCULATE TIME FOR TRACK T TO COLLIDE WITH ALL OTHERTRACKS J x x- I INVENTOR I WILLARD OMEILANDER M M m m ATTORNEYS sET FLAGBIT PATENTEnJuH 6 I972 3, 668,403

sum 9 BF 9 n4 L GROUND I00 I 34m" MAX MlW INVENTOR WILLARD C. MEILANDERmlimmllam ATTORNEYS [No CONFLICTJ FCONFLICTJ METHOD AND APPARATUS FORVEHICLE TRAFFIC CONTROL The annual number of midair collisions hasalmost doubled in the last two years. This is true of military as wellas commercial aircraft. To meet this alarming increase, plans are inprogress to provide automatic conflict prediction. However, the currentapproach involves placing rather extensive and expensive equipmentaboard each aircraft. This costly approach may become a necessity if thesingle alternative is a conventional sequentially oriented ground-basedradar dataprocessing system. For every radar scan in a ground-basedsystem, effective control would require that position, speed, anddirection of every aircraft detected be processed sequentially withrespect to a large number of other aircraft within the surveillancerange of a given radar. Even with the fastest computers presentlyavailable, the sequential approach would immediately place a relativelylow limit. on the number of aircraft that could be handled.

Therefore, as a general object, the invention contemplates solving theair traffic control problem by utilizing an associative processor whichis a digital processor capable of performing common arithmetic orlogical operations on all words in its memory simultaneously, comparedwith the conventional digital processor performance of one operation ononly two words at one time. With the parallel arithmetic capabilityprovided by the associative processor, ground-based automatic conflictprediction becomes feasible and compatable with existing air trafficcontrol facilities.

The invention has a further object to provide collision avoidancemaneuvering techniques, conflict prediction across sector boundaries,and all this being accomplished automatically and simultaneously by thedata processing system.

Essentially, the aforesaid objects of the invention and other objectswhich will become apparent as the description proceeds are achieved byproviding a method for efiecting vehicle collision avoidance whichcomprises the steps of determining continuous vehicle positioninformation rapidly for vehicles within a predetermined area withrespect to a predetermined reference, computing course and speed for allvehicles on the basis of repeated position information for all vehicles,determining course intersect position and time for all vehicles to eachother with respect to a predetermined reference, comparing all vehicleintersect times to a predetermined standard, and sending maneuveringinstructions to all vehicles having intersect times within thepredetermined standard so as to extend the intersect times outside thepredetermined standard.

For a better understanding of the invention, reference should be had tothe accompanying drawings wherein:

FIG. 1 is a block diagram schematic of the overall system conceptshowing the major components;

FIG. 2 is a block diagram illustration of the basic components of theassociative processor of FIG. 1 adapted to achieve the solution to theair control problem;

FIG. 3 is a schematic block diagram of a system to process radar datainformation for utilization in the overall system of FIG. 2;

FIG. 4 is a schematic block diagram of a system for pulse-topulsecorrelation; 7

FIG. 5 is a word format for pulse-to-pulse correlation,

FIG. 6 is an information flow chart for pulse-to-pulse correlation;

FIG. 7 is an information flow chart for pulse-totarget ven'fication andbeam splitting;

FIG. 8 is a block diagram indication of the state progression for targettrack to show how target smoothing and predicting is effected;

FIG. 9 illustrates a typical program that may be utilized to generatethe predicted positions of aircraft simultaneously in the trackersection of FIG. 2;

FIG. 10 illustrates one approach which might be utilized to determinethe threat of vehicle collision, which is the evaluation of flight pathvector intersection;

FIG. 11 is an algorithm of a collision solution utilizing the flightpath vector evaluation of FIG. 10;

FIG. 12 illustrated the buildup of an associative processor wordstructure necessary to implement the algorithm of FIG. 1 1;

FIG. 13 is an example of another algorithm to solve the collisionavoidance problem determining a controlled space zone around eachvehicle; and

FIG. 14 is a block diagram schematic illustrating a typical systemimplementation and the type of collision avoidance or vehicle controlthat can be accomplished.

Essentially, the general approach to the problem is illustrated in FIG.I. Here, an aircraft is illustrated by numeral 10, and positioninformation of the aircraft is generated by a beacon data link 12cooperating with a beacon receiver and transmitter 14 on the aircraft10. The data link 12 may be ground-based, aircraft-based orsatellite-based, as the need demands. The beacon data link 12 is merelyone illustration of the means to obtain aircraft position information,and the invention contemplates that any suitable method to obtain thisinformation will meet the objects of the invention. In any event, theinformation from the data link 12 is sent to a high speed vehicleposition acquisition system 16 which can be of the type illustrated anddefined in my co-pending patent application entitled HIGH SPEED POSITIONACQUISITION SYSTEM AND METHOD," filed May 1, 1969, with Ser. No.821,028. Again, the invention contemplates that any suitable high speedposition information generation system will meet the objects of theinvention, and the system described in my co-pending application ismerely one practical example.

The target position information is then provided as an input to an airtraffic control associative processor indicated generally byblock 18.The associative processor 18 may automatically provide information to betransmitted to aircraft 10 over line 20 through the beacon data link 12.Also, the associative processor will drive a CRT display 22. The CRTdisplay 22 can be broken down into an actual situation display and/or aquery display as is well known to those skilled in the art. In anyevent, a skilled human operator 24 is watching and expertly appraisingthe situation shown on the display 22, and making judgments, ifnecessary to send instructions or information by voice or digitally viaan air trafiic control communications channel 26 or the beacon data link12 to the aircraft 10 by radio transmission. Thus, it should be seenthat the invention contemplates that information may be sentautomatically to the aircraft 10 from the associative processor 18, ormay be sent by the aircraft controller 24 over his communicationsnetwork 26. The invention contemplates that information automaticallysent to the aircraft might be to control appropriate indicators on theinstrument panel of the aircraft to indicate potential collisions,suggested course and/or speed changes to avoid the collision, and anindication of the time to collision, as well as the direction from whichthe potentially colliding aircraft is approaching. The pilot would notnecessarily have to act on this information, but it would be availablefor visual observation in front of him. The information will notautomatically control the aircraft, unless in some cases this might bedeemed desirable. In any event, the invention contemplates that thecontroller 24 will have primary control of the situation, and that hecan also evaluate the information generated by the processor 18 aspresented on his display 22.

The overall arrangement of the data processor 18 is indicated in generalblock diagram form in FIG. 2. The processor 18 is indicated by the largedotted block in FIG. 2, and the functions performed within the processor18 are indicated by the respective blocks indicating radar correlation30, trilateration processing 32, tracking 34, message format 36,maneuvering decision criteria 38, and ground collision avoidance 40. Theinterrelating arrows between blocks 30 through 40 indicate theinformation flow in the processor, all of which will be more fullyexplained hereinafter. The remaining components of the system includeradar sites 42 cooperating with the radar correlation section 30.Trilateration sites 44 cooperate with the trlateration section 32. Amonitor track/flight plan section 46 forming a part of the dataprocessor 18 cooperates with information received from the trackingsection 34 in combination with a bulk store 48 containing flight planinformation. A command function section 50 cooperates with the messageformat section 36 to effect a data link between the control system andthe vehicles being controlled.

In the preferred embodiment of the invention, x y and h positioninformation on aircraft is generated from the information provided bythe trilateration sites 44 to the trilateration processing section 32.As described in my aboveidentified application, section 32 effects aroll call order according to range, indicates site start time forrespective sites to prevent overlap, and effects ordering on the basisof site range calculations for each site with respect to the aircraftassociated with the site. The section 32 also confirms the altitude sentfrom each aircraft by calculation to determine whether altimeters arefunctioning properly.

The identifying x, y and 11 position information is sent from section 32into a tracking section 34 which functions to smooth, predict and updateall aircraft tracks, both those operating under VFR and IF R conditionsat a repetitious rate, selected to be, for example, every 0.2 seconds.The tracking section 34 looks for consistency in the signals receivedfrom section 32 indicating a smooth track of an aircraft, rather thanfalse target information, or erroneous sporatic signals caused by noise,or the like. The target updating information is provided at between 0.2to 3 second intervals based on predicted position as computed by thesection 34, regardless of how frequently actual position is determinedbased on the trilateration section 32 or the radar correlation section30. Normally, actual position measurement by either of the sections and32 will be made on intervals of between about 0.2 to about 10 seconds.The smoothing, prediction, and updating by section 34 can be done by anysuitable mathmatical solution adapted to simultaneous calculation byparallel operation of the associative processor 18. Conventional systemshave difficulty doing this in short periods of time for large numbers ofaircraft, and hence this is where the practical necessity of theassociative processor is extremely important.

The tracking section 34 also receives input information from the radarcorrelation section 30, and likewise provides identify and positioninformation in the x, y and h coordinates for both sections 30 and 32.The reason for providing the identify and position information tosections 30 and 32 is so that particular known targets can beinterrogated at each trilateration site 44, and so that targets beinginterrogated by the trilateration system can be ignored at radar sites42 after processing data through radar correlation section 30.

The purpose of the radar correlation section 30 is to detect thosetargets that don't respond to the trilateration sites 44. These would betargets that are not cooperating because they dont have a beacon system,or their system is not functioning properly, or they are unfriendlyaircraft, etc. The radar correlation section provides in accordance witheach respective radar site 42 a respective radar coverage assignmentdependent upon the terrain, and the actual functional operationalcharacteristics of the radar from each particular site. Each radar sitereports target range and bearing. This information is determined for allcontacts not indicated as being detected by the trilateration sites 44.Essentially, conventional radar systems are utilized with the systemsbeing assigned particular areas, as defined above, depending uponterrain characteristics. The area definition is programmed into thecorrelation section 30 and in efi'ect section 30 decides the radar fromwhich to accept a report, and which radar will back up the reportingradar, and how long a period must expire before backup is necessary. Ifconventional sweep radar is utilized, adjacent radar sites may have todetect that conical area above each respective radar site which cannotbe swept by the conventional radar equipment. The elimination of targetsalready detected by the trilateration sites 44 is easily accomplished inthe associative processor by the identify and position information in x,y and h sent from the tracking section 34 to simply tell the correlationsection 30 that targets do exist at such and such specific coordinatesand to ignore any targets which are detected at those coordinatesbecause they have already been detected. Thus, the radar correlationsection 30 will only detect targets that have not been previouslydetected by the trilateration sites 44 and processed by thetrilateration section 32.

Radar correlation and detection techniques are well known to thoseskilled in the art such as the Navys NT DS system for utilization overwater with ships or the SAGE system utilized by the Air Defense Command.However, these systems operate with conventional computing techniques,and hence do not utilize the parallel processing possible with theassociative processor contemplated by the invention, and hence a largenumber of targets and the time of handling the information cannot nearlyequal that contemplated by this invention.

COLLISION AVOIDANCE DETECTION All target information is passed to thetracking section 34 and hence all target tracks are predicted andcontinuously updated and transferred to the ground collision avoidancesection 40 as well as to monitor 46, which will bermore fully explainedhereinafter. The ground collision avoidance system 40 efiectsdetermination as to whether potential collisions exist or not for allaircraft in real time by an algorithm used in programming and definedmore completely hereinafter. The system also determines if conflicts mayexist if vehicles turn in a certain direction, and sends instructionsnot to turn. This detection also includes intruder detection which is ofaircraft intruding airspace in which they are not authorized to operateas defined by the processor 18. The section 40 provides 20 secondcommand maneuvering devision information to be sent via the messageformat section 36 to the respective aircraft indicating direction ofmaneuver that should be taken to avoid conflict with this being precededby a 40 to 60 second alert indication that may include instructionsintended to prevent aircraft maneuvers that might increase thepossibility of collision in the aircraft for which potential conflictexists. The maneuver decision for IF R aircraft maybe sent through amanual inhibit 40a controllable by an air controller while themaneuvering decision for VFR aircraft may be sent directly to themessage format section 36 for direct transmission to the VFR aircraft.

The ground collision avoidance system section 40 operates in conjunctionwith the maneuver decision criteria section 38 in an operation indicatedby the input identify arrow ID. and the output maneuver option arrowfrom the section 38. In effect, the section 38 will carry predeterminedinformation about every aircraft in the world that is known to exist atthat time with this set of information indicating the maneuveringcapabilities of the aircraft, and in preferred order the type ofmaneuvers most easily executed with least passenger discomfort, withleast strain on the equipment, most economical, and safest for theparticular aircraft being involved. This, when an aircraft type signalis sent from section 40 to section 38, the loop will close by sendingback the preferred maneuver option for that particular aircraft withthat option then being introduced into the solution for collisionavoidance to see if that option will effect a solution. If the firstoption will not solve the problem, the second preferred option will thenbe sent to determine if that will solve the problem. Other potentialsolutions for the aircraft involved will be established and the optimalsolution for each potential conflict between two or more aircraft willbe provided.

The section 40 tests all maneuvers before issuing any instructions todetermine whether the specific maneuver will avoid conflict with allaircraft in the system. The type of maneuvers presently contemplatedinvolve changes in course, speed, and/or altitude. The objective of themaneuvers is to get all aircraft on safe vectors with respect to allother aircraft and maneuvers will not be indicated as commands until anoptimally safety situation is assured by the processor in which nothreats of collision are present.

The maneuvering decision information sent from section 40 through themassage format section 36 may be in terms of actual control of thestructural components of the aircraft to effect the maneuver in anautopilot type situation or may be visual or sound indications to thepilot as to what is suggested or required to avoid possible conflict.The system is designed to operate to give enough alert time with respectto possible conflict so that perhaps the aircraft pilot can effectmaneuvers of his own that will eliminate any necessity for commands tobe sent from the section 40. ln other words, many times if a pilot iswarned about another aircraft in the vicinity, and he can see where theother aircraft is in the vicinity, he can maneuver his plane himselfbased on his prior experience without relying upon the computer to comeup with a new course and/or speed for him to avoid the conflict. In theevent that the alert given to the pilot has not resulted in a safesituation, maneuver instructions will be issued to effect a safesituation (pilots can worsen the situation while trying to help thenegative instructions described hereinafter will correct thispossibility).

it is contemplated that the section 40 will generate only onemaneuvering option, rather than several, with this option being basedupon the best possible course to take to avoid conflict. As mentionedabove, the maneuvering instruction is sent directly to VFR aircraft,while with respect to IFR aircraft, the signal is sent saying that thecomputer intends to instruct the pilot to perform this maneuver, andonly by utilizing the manual inhibit can the person effecting aircontrol change it.

The invention contemplates that these maneuvering decision signals willbe sent to the planes every 0.2 seconds until they are acknowledged bythe pilot or in the case of an autopilot operation until the actualcontrol of the aircraft has been effected.

In a situation involving parallel courses, for example, where a turn byeither aircraft toward the other might create a potential conflict,negative instructions are sent to each plane indicating it is unsafe toturn one direction or the other as the case might be. There are manyother examples besides the parallel course situation where negativeinstructions will be extremely helpful in collision avoidance.

MONITOR SECTION Another portion of the associative processor operationwhich is designed to avoid possible aircraft conflicts involves themonitor section 46. In effect, this section incorporates the filedflight plans for all lFR aircraft in the bulk store 48 for a period oftime, such as for example the next l2 hours. The monitor track section46 then checks all aircraft against their flight plans including flightplan modification inputs 49 as they would normally unfold and determineswhether any possible conflicts will occur because of the filed flightplans. The monitor thus by checking all plans previous to their actualoperation insures that they will clear without any conflict with filedflight plans and sends the signal to the air control command over theline 490 as necessary to indicate flight plan changes that should beeffected. If, for example, a flight plan modification comes inindicating that engine trouble has occurred on the ground and a planewill be leaving minutes behind schedule, that plane could be notifiedthat it should leave minutes behind schedule so as to avoid conflictenroute or at its terminal area, or as a result of overload of theterminal area. This means the plane would stay on the ground 10 minuteslonger thereby conserving fuel and equipment making the operation muchcheaper and more efficient for everyone involved, plus eliminatingpotential conflict situations that might occur at the terminal area.

The monitor section 46 also may send signals to the command 49a on thebasis of signals received from the tracking section 34 that aircraft arenot on their flight plan and that they should effect changes in courseand/or speed to get back on their flight plan, or if it is determinedthat the aircraft cannot get back on their flight plan then to effect achanged flight plan and compare the changed flight plan and all filedplans and other modified plans to determine whether potential conflictswill occur in the future on the basis of this last changed flight plan.It should be understood that the information in the bulk store isupdated whenever new flight plans or changes in any flight plan occurand that this data is a function of time in indicating where planesshould be at predetermined times in accordance with their filed flightplans.

The great advantage of the associative processor 18 is that it can loadinformation in parallel which is a capability not on joyed by any otherexisting processing equipment. and that by loading and processinginformation in parallel. all computationscan be effected simultaneouslyfor all aircraft with respect to conflicts, position determination,maneuvering options, etc., all of which is more fully definedhereinafter with respect to the particular algorithm and conflictdetection logic contemplated.

The specific simultaneous data operation of an associative processor isdescribed in more detail in the above-identified co-pending patentapplication. The operating mode of an associative processor is forparallel read and write capability to effect arithmetic operationsimultaneously on all vehicles. The processor utilizes an associativeprocessing memory, such as shown in Pat. No. 3,391,390 and No. 3,548,386as the basic component. The associative processor can simultaneouslyperform search, logical, or arithmetic instructions with respect to allwords or selected words and/or selected portions of words stored in thememory of associative processor 18. A proper arrangement of theprocessor to accomplish the desired conflict detection and suggestedmaneuvering to avoid potential collisions is described hereinafter.

RADAR DATA PROCESSING GENERAL HO. 3 shows the basic functions requiredin radar-data processing. The radar 99 antenna is assumed to rotate at aconstant rate. Target reports generated by the search radar are firstsubjected to a pulse-to-pulse correlation section 100 that filters outmost of the noise reports. A section 102 to convert to predeterminedcoordinates is optional. The reports that are validated in thisprocedure are next subject to a track while-scan (TWS) procedure insections 104, 106, and 108. This procedure automatically starts trackingand identifies the sources of the reports as ground clutter, noise, ortrue targets. Aircraft within the airspace surrounding the radar aretracked, and track information is presented in real time by section tothe display units. The system to achieve position information bytrilateration to efiect more accurate tracking is better defined in theabove-identified patent application.

PULSE-TO-PULSE CORRELATION The data processing functions included in thepulse-to-pulse correlation section 100 are digital formatting of theradar reports, target correlation and verification, and azimuth beamsplitting. The output of radar subsystem 99 is a tentative targetdeclaration when the receiver output exceeds an automatically adjustedsignal-to-noise ratio. The declaration includes range and azimuth data.Because of the high noise content anticipated in the output of the radar99, a multithresholding procedure is proposed. The target reports aresubjected successively to thresholding criteria (for example, 2 hits outof 3 transmitted pulses, 3 hits out of 5, 4 hits out of 9, and n hitsout of m). A tentative target is accepted and reported when it hits arereceived in less than m transmitted pulses. A true report considered nolonger in the radar beam when n misses are recorded after n hits arerecorded. These data then are used in a beam-splitting operation toprovide a better estimate of azimuth position.

GENERAL This process consists of five principal activities: lscan-toscan correlation of targets, (2) automatic track initiation, (3)smoothing and prediction of positional data for target tracks, (4)clutter rejection, and (5) automatic track declaration.

SCAN-TO-SCAN CORRELATION SECTION 104 As each radar report is presentedto the scan-to-scan correlation section 104, it is compared withpreviously established tracks. If the position associated with thereport agrees, within tolerance, with the predicted position for a giventrack, the report is said to correlate with the track, and the positionof the report is taken to be the current observed position for thetrack. If the report does not correlate with any track, it is used toautomatically initiate a new track. Tracks are terminated ifinsufficient correlating reports are received from scan-to-scan.

In using reports from the trilateration system 44, the proper tracks arelocated by the identity of the reporting aircraft, and the tracks areupdated. However, because of potential noise in the system each newreport is subjected to sufficient tests so that when a report does notexactly coincide with the predicted position the report is validated ifit is within certain limits of the predicted position, these limitsbeing set by the error in the position reporting system and errors intrack processing. The report is further validated if it is withincertain greater limits than those above where these greater limits areset by the acceleration and/or maneuver capabilities of the aircraft. Inthe event a maneuver or change in acceleration is detected, the track isso marked and the existence of maneuver information is used in conflictprediction. If reports from the trilateration system are not validated,they are discarded and a new report is immediately requested during thenext interrogation cycle.

SMOOTHING AND PREDICTING SECTION 106 Smoothing and predicting ofpositional data are performed by a linear smoothing and predictingsection 106. In particular, use is made of the (01,3) tracker discussedby Benedict and Bardner in their paper, Synthesis of an Optimal Set ofRadar Track-While-Scan Smoothing Equations, IRE Transactions onAutomatic Control, July 1962. In addition, we have found that properchoice of smoothing and prediction weighting parameters results in anoptimal linear tracker in the sense of noise reduction and maneuverfollowing capability. Such choice is based on the quality of theparticular track and the maneuvers being executed. An accelerationparameter is added when required to effect smooth performance of thetracker.

It will be evident to those skilled in the art that the weightingparameters 3 will be different for radar track and trilateration tracksbecause of the differences in accuracy of reported position of the twosystems. The trilateration reports are substantially more accurate andare available more frequently.

CLUTI'ER REJECT SECTION 108 The proposed track-while-scan correlationprocedure includes provision for rejecting tracks due to ground clutter.Tracks are identified as due to ground clutter on the basis of theirassociated velocity term. The tracker associates with each track avelocity component in each of the reference coordinates. Tracks due toground clutter have apparent velocity components of low or zeromagnitude. Accordingly, the track-while-scan correlation procedurespecifies a periodic examination of all tracks and the rejection ofthose whose maximum velocity component is less in magnitude than anestablished tolerance, and this is accomplished by section 108.

AUTOMATIC TRACK INITIATE SECTION 1 10 In general, track-while-scansurveillance systems cannot perform automatic track initiation. Thetrack initiate function is usually manual operation in which an operatorindicates a specific radar target to the data processor for tracking.The reason that automatic initiation has not been achieved lies in thelimitations of conventional data processors. The associative processor18 overcomes these limitations and establishes a track for each sensorreport.

An outstanding feature of the track-while-scan correlation procedurelies in a provision for automatic track declaration and for rejection oftracks due to noise. Automatic track declaration and validation areeffected by associating with each track a quality tag that increases upto some terminal value with successive correlations. Tracks whosequality tag exceeds a fixed level are considered to be valid. Validtracks are assumed to represent aircraft and are automaticallydisplayed.

Detecting tracks due to noise presents a formidable problem butfortunately one that need not be solved explicitly. In fact, theautomatic track declaration and validation procedure obviates theproblem. There is a vanishingly small probability that a track due tonoise will achieve a quality tag level associated with a validatedtarget. Hence, by displaying only those tracks whose quality tag exceedsa fixed level, tracks due to noise are automatically rejected.

CORRELATION WITH OTHER SENSORS As proposed, correlation with othersensors is carried out directly in the associative processor 18. Forbeacon inputs, correlation is performed in succession on range,identity, and altitude. A beacon target report is given priority over aradar report; that is, a beacon report rather than a radar report isprocessed in the track-while-scan mode. The beacon in this case may beconsidered to be a scanning system similar to radar, or a trilaterationsystem as defined in the aboveidentified application that providesnearer to continuous tracking by rapid successive sampling.

SITUATION DISPLAY PROCESSING Automated information display techniquesfor the CRT display 22 should provide the display operators 24 with ameans of requesting complex searches on a large track file such as thebulk store 48 or the tracking section 34. The associative processorperforms the complex search operation with an execution time that isindependent of the number of aircraft in the track file. The associativeprocessor stores new data, updates old information, rapidly searches thetrack file, and distributes the requested data to the proper consoles.It can refresh the display screen at a rate that minimizes operatorfatigue.

INFORMATION RETRIEVAL The associative processor-based informationretrieval system which I propose is capable of interrogating a bulkstore 48 in excess of 25 million bitsin less than 0.1 seconds. Eachinterrogation may include a complex pattern of operations. The itemsresponding to the search may also be updated or deleted, if requested.

The associative processor 18 for the information retrieval systemcontains any number of words desired. A bulk storage system is used forthe data base. Parallel readin of data to all words in the associativeprocessor memory is provided through the response store, thus overcominginput/output constraints. These inputs then are processed using thesimultaneous search capability of the associative processor. Theassociative processor, in turn, communicates with the several querystations via a bussing system. These structural features are more fullydefined in application Ser. No. 1,495 filed Dec. 29, 1969, for which Iam a co-inventor.

PULSE-TO-PULSE CORRELATION ALGORITHMS GENERAL Since pulse-to-pulsecorrelation is a significant part of radar-data processing, algorithmsfor performing this operation will now be described. FIG. 4 shows asimplified block diagram of a system configuration for pulse-to-pulsecorrelation. FIG. shows the associative processor word format.

CORRELATION ALGORITHM A target declaration from a radar quantizer 120causes range data to be gated through gate 122 into the comparandregister 124 of the associative processor and starts the correlationprocess, see FIG. 4. A between-limits search on range is made. If nomatch is found, the target declaration is accepted asa tentative newtarget. A search then is made on the bit column of the associativeprocessor target file 126 to locate an empty word and the new target iswritten into the target file at the empty word. The range of target andthe azimuth position are inserted. A one is inserted into the update,acquire-I, and busy-bit columns for the word, as seen in FIG. 5.

If a match is found, a one is merely inserted in the update column forthe word. The operating time required for the execution of eachoperation is indicated outside the lower righthand corner of eachoperation box in FIG. 6. A total of 3.9 p, seconds is required for thecorrelation of a new target and 3.1 u seconds for a previously reportedtarget. These correlations are the only pulse-to-pulse operationsperformed in real time, and are typical times based on the state of theart in the presently known equipment.

TARGET VERIFICATION The target verification and beam-splittingoperations are performed in the dead-time at the end of the radar pulserepetition period and require 18 .1. seconds for all the targets (seeFIG. 7).

'A search is made on the update and acquire-I bits. This search locatesall tentative targets that have received a hit during the radar pulserepetition period immediately prior to the search. A one is added to thesummation of hits field for all of such words. This operation takesplace simultaneously in parallel for all words.

Next, a search is made on the azimuth field to locate those targets forwhich the stored target azimuth is equal to the current azimuth in theazimuth counter, less 3. This search will locate all targets that werefirst reported 3 pulses before the current transmitted pulse. A searchfor a number less than two then is made on the summation of hits inrange field and this search is logically anded with the previous search.The result is to locate all targets that fail a 2 hits out of 3transmitted pulses acceptance threshold. These targets then are regardedas false targets and deleted from the associative processor target file126. This procedure is repeated to implement thresholds of 3 hits out of5, 4 out of 9, and n out of m. The multiple threshold filtering isproposed because of the high noise level anticipated from the radar.

The next operations locate targets for which it hits have been receivedin less than m transmitted pulses. Such targets are considered truetargets. The acquire-II bit is set to one to indicate this fact. iftarget reports are not received (misses), they are now counted for thesetargets. This procedure is carried out by searching for targets thathave the acquire-II set, but not the update bit set.

When n misses are received, the target is considered to no longer existin the antenna beam. Adding the increment of current azimuth to thestored increment of acquire azimuth, dividing by two, and subtractingthis from current azimuth provides the best estimate of the true azimuthposition in the azimuth field (beam-splitting operation). The targetword now can be read out for subsequent coordinate transformation andscan-to-scan operations.

The remaining components of the system of FIG. 4 are a time reference128, a range counter 130, an azimuth encoder 132, and an azimuth counter134. The associative processor file 126 can be a component of the radarcorrelation function 30, or a separate associative processor at radarsite 42.

TRACK-WI-IILE-SCAN ALGORITHMS GENERAL ACQUISITION AND CORRELATION Aseach radar report is presented to the data processing system, it iscompared with previously established tracks. Each track is kept in anassociative word, which in part has the following form:

Field 9 8 6 5 4 3 2 1 Contents it 5' h x y 11,, x y I: Fields 3, 2 and 1contain x, y and h, respectively, the current observed coordinates forthe track (that is, the observed coordinates of the target associatedwith the track). Fields 6, 5, and 4, contain .i,,, y,,, and lirespectively, the current predicted coordinates for the track (that is,the coordinates at which the track target is expected next to be seen).Fields 9, 8, and 7 contain .t', y, and h, respectively, the currentdirectional velocities for the track. Smoothing of observed positionaldata, and computation of predicted positions and velocities areaccomplished by means of the (a, ,8) tracking equations discussed below.

If the position associated with the report agrees, within tolerance,with the predicted position for a given track, the report is said tocorrelate with the track, and the position of the report is taken to bethe current observed position for the track. If the report does notcorrelate with a track, it is used to automatically initiate a newtrack. Tracks are terminated if insufficient correlating reports arefound from scan to scan.

The method of initiating and maintaining a track is as follows: when aradar report is received that correlates with no established track, itis used to initiate a new track, and the new track is said to be inState 1. A large square box of V miles (see FIG. 8) is centered aboutthe position of the report, and subsequent to the next sweep of theradar, a check is made to see if any new report lies in the box. If so,the new report is said to correlate with the newly established track.Smoothed position and velocity values are calculated to update thetrack, and the track is advanced to State 2. A smaller square box of Wmiles is then centered about the predicted position for the next reportfor the track. Subsequent to the next sweep of the radar, a check ismade to see if any new report lies in the box. If so, the new report issaid to correlate with the track. New smoothed position and velocityvalues are calculated to update the track, and the track is advanced toState 3. The process continues in the same fashion, with smaller boxesbeing used as track quality increases. State values for a track increasewith each successive correlation up to terminal state.

FIG. 8 presents a fiow chart for a seven-state tracking procedure,showing how a target track would progress from state to state. In theassociative processor implementation of the acquisition and correlationprocedure, state values are accounted for by associating with each tracka quality tag that reflects the current track state. Tracks whosequality tag indicated progression beyond a certain state, in particularState 5 of FIG. 8, would be considered valid and in fact to representaircraft. Such tracks would automatically be accepted and displayed. Thechoice of box size used in the correlation search depends on trackquality, accuracy of reported target position, and maneuveringcapabilities of the target.

The flow chart in FIG. 8 indicates how a track passes from state tostate as successive correlations with reported targets are made. Thesize of the search boxes used in the correlation process decreases astrack quality increases with successive correlations. Provision can bemade for increasing the size of the search boxes if, due to maneuvering,the target associated with a track cannot be found in the search boxassociated with the present track state. The provision for increasingbox size for a track when no correlating return is found is not meant toaccount for the case where a target is missed by the radar acquisitionsystem rather than by the failure of the correlation algorithm.

Where a correlation fails to occur because a target is missed by theradar acquisition system, it is not desirable to increase the search boxsize. This might produce an apparently correlating report, which wouldbe due to noise or the target for a different track. A possibleprocedure in the case of a missed radar report would be to assume thatthe planes position is at the latest predicted position and to continuethe smoothing and prediction scheme on that basis, with a modificationmade in the measure of the track quality.

However, the implementation of such a procedure presents obviousdifficulties. When a correlation fails to occur, it is not known whetherthe failure is due to the target's maneuvering, failure of the radaracquisition process, or other causes. Hence, a decision-making processmust be evolved for selecting the policy to be used in the correlationprocess when a track cannot be correlated with a radar report during onesweep of the radar.

A possible policy is as follows: first, limit the increase in box sizeallowed in the attempt to achieve correlation. For example, if a State 7track fails to correlate using a z-size, allow the box size to increaseonly up to a .r-size box. Second, for each target track in State 3 orbeyond, assume the correlation failure to be due to radar fault, reducethe track state by one, set the present position of the target to be thepredicted position, and compute a new predicted position. Third, deletethe target tracks in State 1 that failed to achieve correlation.

If correlation fails with a box corresponding to the current trackstate, but correlates with a lower track state, assume the radar reportwas missing for the current track, and continue to predict on pastinformation while reducing state or track quality. Further assume aswell that the aircraft was turning and establish a second track startingfrom the correlated predicted position. The decision to start a secondtrack will be dependent on the track quality state of the near tracksuch that tracks of low quality will not initiate new tracks but highquality tracks will. In this manner, turning tracks will be retained,and the maneuver detected. This bifurcated tracking process will retainmaneuvering targets in an optimal fashion.

SMOOTHING AND PREDICT ING Smoothing and predicting of positional datawill be performed by a linear smoothing and predicting scheme. Inparticular, the tracker assumed is the (01,3) tracker discussed byBenedict and Bardner in their paper Synthesis of an Optimal Set of RadarTrack-While-Scan Smoothing Equations, IRE Transactions on AutomaticControl, July, 1962. The (01,3) tracker consists of the following set ofequations:

where time derivative n' observed position I n'" smoothed position 11"predicted position, and B weighting factors T time interval betweenobservations Benedict and Bardner showed that choosing ,B=a/2 results inan optional linear tracker in the sense of noise reduction and maneuverfollowing capability.

It is assumed that, in the TWS system, the time interval T of theequation above is constant. The assumption of a constant T tends tointroduce a discrepancy between predicted and observed position of aplane being tracked, since only rarely will the time be constant betweenobservations of the plane by the radar. My estimate of the maximumdiscrepancies indicates they are not significant in TWS, when an updaterate of 0.2 seconds is used.

Improvements in the tracking algorithm are developed by adding anexpression for acceleration when it is determined that accelerationexists The acceleration term is of the form:

n n-l 'Y/TZ n pl) and then the expression for the predicted positionbecomes:

, pu+1 Tag" 7 Acceleration criteria and values of 'y exist when a turnis detected and the acceleration terms are 0 when a turn does not existor at its conclusion, as based on repeated evaluation of velicity.Further, the values of 01,8 and 7 are chosen so that the filter isadaptively optimized for maximum stability in velocity by examination ofthe error in predicted position, and predicted speed, and the trackquality. I have found that the values of afiand y are best determinedexperimentally, and this is well within the ability of one skilled inthe art.

It will be apparent to one skilled in the art that the values ofweighting function a, B and y will be different for radar tracks and fortrilateration tracks because of the differing precision of the twosensors and because of the differing sampling times.

While these many tests to establish the proper weighting functions aredifficult in conventional processors, they are easily accomplished in anassociative processor. In the implementation following, while theacceleration terms are not shown nor are the decision criteria for 01,3,and 7 shown, it will be obvious to one skilled in the application of anassociative processor that these steps are easily implemented.

It should be remembered that while only one coordinate is consideredabove the other coordinates with possible cross coupling terms must betreated to establish the best possible velocity vector and thus the bestprediction of future position.

IMPLEMENTATION ON ASSOCIATIVE PROCESSOR The (01,3) tracker is to beimplemented on the AP. A program has been written to effect thisimplementation. A listing of the program is given in FIG. 9. Astep-by-step commentary on the program follows:

Each target track is kept in an AP word, which in part has the followingform:

Field 9 8 6 5 3 3 2 1 Contents A h y, h,, x y Ii Fields 3, 2 and 1contain x, y and h, respectively, the current observed coordinates forthe track (that is, the observed coordinates of the target associatedwith the track). Fields 6, 5 and 4 contain x y, and h,,, respectively,the current predicted coordinates for the track (that is, thecoordinates at which the track target is expected next to be seen).Fields 9, 8 and 7 contain x, y and h, respectively, the currentdirectional velocities for the track. Smoothing of observed positionaldata and computation of predicted positions and velocities areaccomplished by means of the (afi tracking equations discussed above andthe AP program listed in FIG. 9. Each step of the AP program is to beexecuted concurrently for all tracks ready for positional updating atthe time of program execution.

Step 1 is started at an appropriate time and specifies for all tracksthe operation:

k 11; U That is, Field F is subtracted from Field F and the result isplaced in Field F giving in Fields F F and F the quantities x x,, y y,,,and h h,,, respectively. Fields not specified in Equation (1) are notaffected. In the step-by-step listing of FIG. 9, only the fields whosecontents results from the present operation (step) are displayed at eachstep.

Step 2 specifies for all tracks the operation:

a1-,,-F,,uF,,; =1,2,3 2 That is, Field F is multiplied by the determinedvalues of a, and the result is placed in the union of Fields F and FField F, is provided to account for scaling in the product a F Hence,Step 2 results in Fields F F and F containing the scaled products aux,x,.,),a(y,, y and 01(h, h, respectively. Fields not specified inEquation (2) are not affected.

Step 3 specifies for all tracks the operation: I k$ J U! r )1 That is,Field F, is added to Field F and the result is placed in Field F givingin Fields F F and F the smoothed pgsitions f. m t -l)1 in =yp-1 m fir.)and a h,-, a( h, h,,.,), respectively. Fields not specified in Equation(3) are not affected.

Step 4 specifies for all tracks the operation:

B/T' r' la mj= (4) That is, Field F is multiplied by the determinedvalues of Bl T, and the result is placed in the union of Fields F and FField F is provided to account for scaling in the product B/T- F Hence,Step 4 results in Fields F F and F containing the scaled products B/T(x,x [3/70, y, and /5'/T(h, hp-l), respectively. Fields not specified byEquation (4) are not affected.

Step 5 specifies for all tracks the operation:

Jl k3 J1; This is, Field F is added to Field F and the result is placedin Field F giving in Fields F F and F the updated smoothed y eloc itiesL i B/T(x,, x, 37,, j B/T(y,, y,,.,), and h h +B/T(h, h respectively.

The subscript u is used to indicate that the values have been updatedduring the present execution cycle of the program. Fields not specifiedin Equation (5) are not affected.

Step 6 specifies for all tracks the operation:

T-F F,;,UF,,;j=7,8,9 (6) That is, Field F is multiplied by the constant(comparand) T, and the result is placed in the union of Fields F n and FField F n is provided to account for scaling in the product T F Hence,Step 6 results in Fields F F and F containing the scaled products T1,,Ty m and Th respectively. Fields not specified by Equation (6) are notaffected.

Step 7 specifies for all tracks the operation:

1 J That is, Field F J is added to Field F and the result is placed inField F giving in Fields F F, and F, the updated predicted positions x,I T2, y, i Ty and h,,, F 17i,,, respectively. The subscript u is used toindicate that the values have been updated during the present executioncycle of the program. Fields not specified by Equation (7) are notaffected.

Step 8 specifies the operation:

an F21 F1!) That is, new observed values of Track Coordinates x, y, andh are inserted into Fields F F and F respectively. This occurssubsequent to track correlation and at any time prior to thesimultaneous updating of all tracks.

Step 9 specifies transfer of control to the main program.

It should be remembered that the above steps are carried outsimultaneously for all the tracks in the system.

COLLISION AVOIDANCE ALGORITHMS INTRODUCTION This section describes twomethods for handling collision avoidance in the Associative Processor(AP). Method 1 involves a two or three dimensional equation of thepoint/slope form that describes the flight path for each target. Method2 is a more sophisticated three dimensional approach that considers thecontrolled air space around each aircraft and expands this air space forfuture predictions to take care of the expanding uncertainty in aircraftpositions.

METHOD 1 Assume that the flight paths of two aircraft 1 and 2 aredescribed by the slopes and equations of FIG. 10. In H6. 10, theequations are of the point/slope form where the slope a A y/A x, but Axit and Ay y'r. Hence, for the same time in terval, a a ls.

lfx, and y, are the coordinates of a target at any given time, a can befound as above and b can be found by b=y. ax,.

The potential point of collision (x,, y,) can be found by solving thisset of equations:

y a,x b, y w

Only the solution for x is needed since only one of the two coordinatesis used in the calculation of time for each target to intersect thepaths of each of the other targets.

With the above background, consider FIG. I 1, the collision avoidancealgorithm flow chart for Method 1, which has the following steps:

1. Periodically extract a track Tfrom the track file and calculate itsslope at, and y intercept b 2. Examine a if it is less than I, proceedto Step 3; if it is not, then go to Step 4; keeping af less than 1avoids the case where af' approaches infinity.

3. Calculate slope a," and y-intercept b," for all targets, and go toStep 5.

40 4. If "0 is not less than i, switch T and all other tracks toequations having the form x =ay b and solve for a and b.

5. Determine if I a, a,- K, where a, is the slope for each of the othertargets, a is the slope for T, and K is some predetermined constant;this is done to determine if target i is flying a path that is parallelto that of T. If parallel, i.e., a, a, K, then proceed to Step 16; ifnot, proceed to Step 6.

6. Calculate x a potential coordinate of collision, for each of theother paths with the path of T:

lfx, in Step 3 or y, in step 4 are zero, the value x, will be 1: This isthe case where an intercept does not exist and the intercept x, =x,.

7. Calculate the time for track T to collide with all other tracks:

l2. Determine if I, 2 minutes in those tracks that remain; if yes, setflag bit rfor each response.

13. Determine if a new I, has been calculated. lf Step 13 rather thanStep 9 is being performed, it has been; if yes proceed to Step 14; ifno, proceed to Step l0.

l4. Proceed to Step 15 only for those targets having flag bit r set; ifr is not set for any target, exit.

15. if r, is set, determine if I I r, I 1 minute; if yes. a maneuverdecision is determined as indicated by block 40 of FIG. 2.

The first preferred maneuver is applied to one of the aircraft inconflict and the aircrafts future position and velocity vector iscalculated for a time of 1 minute. This position is then inserted as inStep 1 above and all aircraft are updated for one minute at theirpresent velocities. The tests are performed to establish a conflict freesituation. If this situation exists the maneuver decision is transmittedto the aircraft or to the controller as mentioned above.

If the situation is not conflict free, different maneuvers are testedand applied to both aircraft until an optimal set of maneuvers providesa conflict free situation.

16. If flight paths are essentially parallel, determine if yinterceptsare less than 3 miles apart; if no, conflict is not imminent.

17. If less than 3 miles, determine if the time for the aircraft to meetis less than 1 minute; if yes, proceed as in Step 15 above.

In the above explanation, the following should be noted:

I. The values of the constants are merely best-guess at this time andcan easily be changed.

2. Sign bits of velocity vectors can be accounted for, but for ease inunderstanding the method rather than minute details, they have not beenconsidered in the explanation.

3. Altitude has not been included, but where this parameter isavailable, the following calculation can be made for each target if acollision is imminent in x and y:

li altitude at potential point of collision for target i,

h, present value of altitude for target i,

Ii, rate of altitude change of target i, and

t, time to reach potential point of collision for target i.

If I h h, k, where 11,. altitude at potential point of collision fortarget T, and k is a predetermined threshold, then a collision isimminent.

FIG. 12 shows the buildup of the associative processor word structurefor a given target necessary to implement the collision avoidancealgorithm. The step numbers and resulting word correspond to the stepsas numbered on the flow chart. Since position coordinates and velocityinformation is already in the associative processor word for otherfunctions, they are not shown here.

METHOD 2.

Another method places a box of safe air space centered about eachaircraft. The sides of the box extend the minimum safe separationdistances in three dimensions from each aircraft. The size of the boxexpands in three dimensions with time to take care of the expandingpositioned uncertaintly as aircraft positions are predicted farther intothe future. The aircraft positions are then predicted into the futureand the possibility of collision exists if any one aircraft will violatethe safe air space box of another aircraft within some safe warningtime. I

Let one aircraft be at x y,,, 11 flying at velocities .i [1 and anotheraircraft be at x,, y,, h, flying at velocities i 5,. it is desired todetermine if one aircraft will violate the air space of the other withinsome time interval (0,7'). The cone trolled airspace around one aircraftis i-A it), M at current time and expands with velocities A A A, to takecare of the expanding uncertainty as aircraft positions are predictedfarther into the future.

There will be conflict if and only if the following three inequalitiesare simultaneously satisfied for some time t a 0:

The easiest way to find whether such a 1 exists is to compute a minimumand maximum r for each inequality and compare. Thus, if

1 1 =minimum time satisfying 2-l r 1 maximum time satisfying 1 2 minimumtime satisfying t,,,,, 2 maximum time satisfying t,,,,,, a minimum timesatisfying r 3 maximum time satisfying then there is a conflict withinthe time interval 0 to T if and y Maximum 1 mlll 1 mln 2a lnl" 3) g um:ll um: 2v um: 37 2-3G Inequality 2-l is equivalent to the following pairof inequalities:

a an x0 A,

Note that A and B will always be defined it A, is fixed so that it isnot a multiple of the resolution of A", and in.

Now consider three cases: i X,, A, 0, A .i', .i}, A,,andi,.\",,-A, 0.

In the first case (i, .i',,+ A, 0), it, ,i,, -A, also 0; 2-6 and2-6abecome B I; A and ill!" I :01am 1 A- In the second case A :r, .i', A2'-6 and 2-6a become/I 1 -B,and a llllll l 1 2 1l a nuu'1 T If this caseis divided into three subcases: x, x, A A x x, A,, and x, -x, A thenfrom the following,

It is seen that the choice of A or 8 depends on x, -x,. In the middlesubcase, it does not matter whether A orB is picked since both arenegative and the effect of the choice will be masked out when inequality2-3a is checked.

In the third case, x, x,, A, 0, .r, -)z,, A, 0, and 2-6 and 2-6a becomeA t B, so

mm 1 =A' 2 l3 um: l Using 2-2 and 2-3 the same way, similar equationscan be developed for t,,,,,, I t,,,,,, and I FIG. 13 shows the resultingalgorithm for collision avoidance. This can be preformed in anassociative processor in parallel (one aircraft x,,, y,,, h against allothers (.x,, y h,). Since the most significant digits of the quotientare formed first in division, the quotient formation can be combinedwith the maximum and minimum operations in Boxes 1, 2, 3; and 4 in FIG.13 and need notbe explicitly stored. In general, some associativeprocessor words will be in Box 1, others in Box 2, others in Box 3, andothers in Box 4 simultaneously. The operations can be carried outsimultaneously.

METHOD 3 Another method which will be evident to those skilled in theart develops the closest point of approach of one aircraft with another.This closest point of approach is obtained by evaluating the derivativesof the paths of the aircraft. Whenever a closest point of approach isless than a critical distance, corrective maneuvers are evaluated andcommands issued as above.

METHOD 4 A further method similar to the above, evaluates the minimumseparation along each of the coordinates established with respect toones of the aircraft and uses such minimum to determine the possibilityof collision. Appropriate maneuvers then take place.

CONTROLLER SECTOR OVERLOAD FAA regulations limit the number of aircraftin one sector to a specified maximum ,value at any one time. Asdescribed above with reference to FIG. 2, the monitor section defineshow the associative processor can be used to determine all the IFRaircraft within a given sector at some future time. The procedure forthis operation extrapolates each aircraft in time along its flight path,and then searches within the boundary of each sector as a function oftime to determine if more than the allowable number of aircraft willexist within any sector at any future time.

TERMINAL OVERLOAD The extrapolation of all filed flight plans withmodifications required in flight, as described above, will lead to anevaluation of aircraft arrival at each terminal area as a function oftime. Terminal load handling capability can be evaluated on the basis ofscheduled takeoffs and landings and predicted weather. Overloadconditions, when established, can be corrected through evaluations of,and necessary modification to each flight plan. Consideration is givenfirst to flights in the air and near the terminal, second to airborneflights far from the terminal, and third to flights on the ground. Suchconsideration involves slowdown or speedup (within limits) of airborneflights and delays at ramp for planned flights. A procedure of this kindpermits minimum fuel costs and delays.

OVER OCEAN COLLISION AVOIDANCE AND CONTROL Navigational satellitesplanned for some future time can provide for over ocean control with thesame equipment used in overland, enroute, and terminal areas. Thesatellites can be either low or stationary orbit. The system envisionedfor this type of overall system is shown in FIG. 14 of the drawings, and

would have a ground station which would discretely interrogate eachaircraft and measure distance from at least two satellites 102 and 104.The system could measure aircraft rapidly using the trilaterationapproach of my above-identified application by using the air controlcenters 106 and 108, respectively. Ambiguities would be resolved bymaintaining the track of each vehicle, while conflicts will be evaluatedas described above. Avoidance maneuvers could be transmitted via abeacon satellite system or alternatively could be communicated by voicefrom ground station 100. This same type of satellite oriented systemmight also control navigational problems for ships 1 14 on a body ofwater 1 16.

WEATHER AND TERRAIN AVOIDANCE It should also be understood that thistype of system could plot weather 110 derived from weather observationsources and advise planes how to avoid same. The system could also plotterrain such as mountains 112 and tall structures 113 and averageterrain elevation, and advise the respective aircraft to avoid theseterrain features based on their plotted positions versus the aircraftsactual position.

Since severe weather which may adversely effect aircraft is bounded,areas of weather are defined by boundaries. Such boundaries are similarto the boundaries of a sector discussed above, and conflict with weatheris established by extrapolating flight plans to determine if theyintersect severe weather areas in a manner similar to the detection ofsector overload.

Terrain avoidance is accomplished by establishing a grid structure in xand y say, every 5 miles. Thus, an area 100 X 100 miles would be amatrix of 20 X 20 or 400 positions. Within each position of the matrixwould be inserted the maximum terrain elevation above sea level withinthe defined 5 X 5 mile area. Aircraft velocities are used to predictfuture position and altitude, and the aircraft position and altitude arecompared with the matrix to determine if the aircraft is too near theterrain. If so, an up command is issued.

Intense weather formations could be stored in the associative processoras an area. Each aircraft when updated and checked for conflict withother aircraft would also be checked for intersection with hazardousweather areas by determining if the aircraft vector intercepted anydescribed weather areas. Routing around weather would be suggested bythe controller and the suggested change would be checked for conflictbefore transmission to the respective aircraft. The flight plan for theaircraft would be modified if necessary and inserted into the monitorsection 46 of the associative processor.

SUMMARY Hence, it is seen that the invention provides a method for rapidevaluation, decision and maneuver particularly designed for aircraft toavoid collisions. In the event of detection of a potential collisionwith another aircraft, a particular algorithm would control theoperation of the associative processor to evaluate a fixed set ofmaneuvers in order of best maneuverability for the particular aircraftto determine an acceptable maneuver. Each maneuver would result in a newvector, and this vector would be evaluated against all other vectors tosee if additional conflicts would occur. The most desirable maneuverthat is safe would be indicated to the controller for his executionalong with a display of the situation and necessary information abouteach of the aircraft. In the event an aircraft approaches too close toterrain, a pullup order would be indicated to the controller withinformation necessary to communicate with the aircraft. It must beremembered that in any case, the controller could be left out of theloop and the plane or planes involved could be directed by the computer.

On detection of conflict in flight plans, modification of the conflictcan be resolved by operating with the standard procedure. Such proceduremay start by delaying flights on the ground. An increase in departuretime or other control situations would be utilized to find an acceptabletake off time. An alternative would be to speed up or slow down involvedaircraft which are airborne. The results of each of the flight planmodification would have to be evaluated by the monitor system shown inFIG. 2 to see that other conflicts did not arise. Conflicts in flightplan which did not result in terminal overload could be easily treatedin the airborne case to achieve minimum cost and time.

The envisioned system preferably requires each aircraft to utilize atransponder of a type similar to those currently available to providefor coverage of all aircraft. If the satellite system is utilized, itlikely would be less costly than the cost of one air to air collision.The satellite system could also provide for surface vessel conflicts.Minimum flight delays could be achieved, and minimum flight operationalcosts could be realized.

While in accordance with the patent statues, only the best knownembodiment of the invention has been illustrated and described indetail, it is to be particularly understood that the invention is notlimited thereto or thereby, but that the inventive scope is defined inthe appended claims.

What is claimed is:

l. A method for effecting vehicle traffic control which comprises thesteps of a. determining vehicle position information in x, y andhrapidly and accurately sequentially for each vehicle within apredetermined area with respect to a predetermined reference coordinatepoint,

b. computing course and speed for all vehicles simultane ously on thebasis of the position information determined y p c. computinginterrogation rate for all vehicles as a function of their positionrelative to predetermined points or their potential collision with othervehicles,

d. determining course intersect positions and time for all vehicles withrespect to each other related to the predetermined reference,

. determining the difference in arrival time of each of the vehicles attheir respective intersect points,

f. determining the minimum separation distance or closest point ofapproach of vehicles with respect to their positions and velocities,

g. comparing the difference in all vehicle intersect times to apredetermined standard, and

h. sending maneuvering instructions to all vehicles having intersecttimes within the predetermined standard so as to extend the intersecttimes outside the predetermined standard.

2. A method according to claim 1 where steps (d) though (g) are allperformed simultaneously for one vehicle with respect to all othervehicles byon associative processor, and where such steps aresimultaneously performed sequentially on all other vehicles.

3. A method according to claim 1 where each of steps (a) through (h) arecontinuously repeated for each vehicle within the predetermined area atnot greater than 6 second intervals.

4. A method according to claim 1 where course and speed intersects forall vehicles are determined by i. defining each vehicle track in termsof slope with respect to an x, y coordinate system with thepredetermined reference at the x, y zero point of the system,

j. determining the potential x, y coordinate of track intersect of eachvehicle with respect to every other vehicle,

k. determining the time when each vehicle is going to reach respectivex, y coordinate of track intersect,

l. comparing to a predetermined time standard the time difference ofeach vehicle reaching its respective x, y track intersect coordinatewith the other vehicle for each intersect coordinate, and

m. indicating which vehicles have track x, y intersects where the timedifference of intersect is less than the predetermined standard.

5. A method according to claim 4 which includes effecting a slopecomparison of the track of each vehicle to determine if the vehicles aremoving on substantially parallel, toward,

away, diverging, or converging paths before accomplishing steps (j)through (m), and only effecting steps (j) through (in) on those vehicleswhose slopes indicate parallel toward and converging courses.

6. A method according to claim 5 where the vehicles are aircraft andwhich includes effecting an altitude comparison to a predeterminedminimum standard of those vehicles which indicate track intersect withinthe predetermined time standard and efiected some collision warningsignal and suggested maneuvering to the vehicle operator for thosevehicles which will intersect within the predetermined altitudestandard.

7. A method according to claim 1 where vehicle position infonnation isdetermined by at least two satellites operating in coordinate relationto each other.

8. A method according to claim I which includes the step of predictingan overload of vehicles in the area as a whole, and at any specificlocations within the area.

9. A method according to claim 8 where the vehicles are aircraft andwhich includes storing all filed IFR flight plans, comparing each IFRflight plan as it is filed with all previously filed lFR flight plans todetermine potential future conflict, and comparing all changed andaltered IFR flight plans to all filed lFR flight plans to determinepotential future conflicts, and providing information in cases wherepotential future conflict is predicted to change flight plans or actualflight paths so as to avoid such conflict.

10. A method according to claim 8 which includes the steps ofdetermining weather and terrain characteristics for the area, andevaluating and controlling the path of all vehicles in the area to avoidcollision of the vehicles therewith.

11. A method to effect vehicle traffic control which comprises the stepsof I I a. determining vehicle position information in x, y and h rapidlyand accurately forvehicles within a predetermined area with respect to apredetermined reference coordinate point,

b. simultaneously computing course and speed for all vehicles on thebasis of repeated position information for all vehicles,

c. sequentially computing whether vehicles will approach within acertain minimum distance of each other,

d. sequentially computing alternate safe courses and/or speeds for allvehicles that have predicted approaches within the predetermined minimumdistances, and

e. sequentially sending maneuvering instructions to all such vehicles tomake their approaches to all other vehicles fall outside thepredetermined minimum standard.

12. A method according to claim 1 l which includes determining vehiclevector intersect points,

measuring the time difference of vehicle arrival at such intersectpoints and comparing it to a predetermined standard, and

providing maneuvering instructions for those vehicles which indicatedintersect within the predetermined standard.

13. A method according to claim 11 which includes determining thedistances of the closest point of approach of each vehicle to each othervehicle based on their computed vector paths, comparing the determineddistances to a predetermined standard, and providing maneuveringinstructions for those vehicles which indicate distances within thepredetermined standard. v

14. Apparatus for effecting traffic control of vehicles which comprises,

means to determine the position of all vehicles within a predeterminedarea,

means to simultaneously determine potential conflicts of each vehiclewith every other vehicle in the area,

means .to simultaneously predict a safe course to avoid potentialconflicts between each vehicle whose path indicates a potential conflictwithout creating a conflict with any other vehicles, and to sequentiallyperform this step for every vehicle and

1. A method for effecting vehicle traffic control which comprises thesteps of a. determining vehicle position information in x, y and hrapidly and accurately sequentially for each vehicle within apredetermined area with respect to a predetermined reference coordinatepoint, b. computing course and speed for all vehicles simultaneously onthe basis of the position information determined by step (a), c.computing interrogation rate for all vehicles as a function of theirposition relative to predetermined points or their potential collisionwith other vehicles, d. determining course intersect positions and timefor all vehicles with respect to each other related to the predeterminedreference, e. determining the difference in arrival time of each of thevehicles at their respective intersect points, f. determining theminimum separation distance or closest point of approach of vehicleswith respect to their positions and velocities, g. comparing thedifference in all vehicle intersect times to a predetermined standard,and h. sending maneuvering instructions to all vehicles having intersecttimes within the predetermined standard so as to extend the intersecttimes outside the predetermined standard.
 2. A method according to claim1 where steps (d) though (g) are all performed simultaneously for onevehicle with respect to all other vehicles by an associative processor,and where such steps are simultaneously performed sequentially on allother vehicles.
 3. A method according to claim 1 where each of steps (a)through (h) are continuously repeated for each vehicle within thepredetermined area at not greater than 6 second intervals.
 4. A methodaccording to claim 1 where course and speed intersects for all vehiclesare determined by i. defining each vehicle track in terms of slope withrespect to an x, y coordinate system with the predetermined reference atthe x, y zero point of the system, j. determining the potential x, ycoordinate of track intersect of each vehicle with respect to everyother vehicle, k. determining the time when each vehicle is going toreAch respective x, y coordinate of track intersect, l. comparing to apredetermined time standard the time difference of each vehicle reachingits respective x, y track intersect coordinate with the other vehiclefor each intersect coordinate, and m. indicating which vehicles havetrack x, y intersects where the time difference of intersect is lessthan the predetermined standard.
 5. A method according to claim 4 whichincludes effecting a slope comparison of the track of each vehicle todetermine if the vehicles are moving on substantially parallel, toward,away, diverging, or converging paths before accomplishing steps (j)through (m), and only effecting steps (j) through (m) on those vehicleswhose slopes indicate parallel toward and converging courses.
 6. Amethod according to claim 5 where the vehicles are aircraft and whichincludes effecting an altitude comparison to a predetermined minimumstandard of those vehicles which indicate track intersect within thepredetermined time standard and effected some collision warning signaland suggested maneuvering to the vehicle operator for those vehicleswhich will intersect within the predetermined altitude standard.
 7. Amethod according to claim 1 where vehicle position information isdetermined by at least two satellites operating in coordinate relationto each other.
 8. A method according to claim 1 which includes the stepof predicting an overload of vehicles in the area as a whole, and at anyspecific locations within the area.
 9. A method according to claim 8where the vehicles are aircraft and which includes storing all filed IFRflight plans, comparing each IFR flight plan as it is filed with allpreviously filed IFR flight plans to determine potential futureconflict, and comparing all changed and altered IFR flight plans to allfiled IFR flight plans to determine potential future conflicts, andproviding information in cases where potential future conflict ispredicted to change flight plans or actual flight paths so as to avoidsuch conflict.
 10. A method according to claim 8 which includes thesteps of determining weather and terrain characteristics for the area,and evaluating and controlling the path of all vehicles in the area toavoid collision of the vehicles therewith.
 11. A method to effectvehicle traffic control which comprises the steps of a. determiningvehicle position information in x, y and h rapidly and accurately forvehicles within a predetermined area with respect to a predeterminedreference coordinate point, b. simultaneously computing course and speedfor all vehicles on the basis of repeated position information for allvehicles, c. sequentially computing whether vehicles will approachwithin a certain minimum distance of each other, d. sequentiallycomputing alternate safe courses and/or speeds for all vehicles thathave predicted approaches within the predetermined minimum distances,and e. sequentially sending maneuvering instructions to all suchvehicles to make their approaches to all other vehicles fall outside thepredetermined minimum standard.
 12. A method according to claim 11 whichincludes determining vehicle vector intersect points, measuring the timedifference of vehicle arrival at such intersect points and comparing itto a predetermined standard, and providing maneuvering instructions forthose vehicles which indicated intersect within the predeterminedstandard.
 13. A method according to claim 11 which includes determiningthe distances of the closest point of approach of each vehicle to eachother vehicle based on their computed vector paths, comparing thedetermined distances to a predetermined standard, and providingmaneuvering instructions for those vehicles which indicate distanceswithin the predetermined standard.
 14. Apparatus for effecting trafficcontrol of vehicles which comprises, means to determine the position ofall vehicles withIn a predetermined area, means to simultaneouslydetermine potential conflicts of each vehicle with every other vehiclein the area, means to simultaneously predict a safe course to avoidpotential conflicts between each vehicle whose path indicates apotential conflict without creating a conflict with any other vehicles,and to sequentially perform this step for every vehicle and means topass potential conflict information to the vehicles and information toeffect a change in path and/or speed to avoid the potential conflict.15. Apparatus according to claim 14 where the means to simultaneouslydetermine potential conflicts and simultaneously predict a safe coursein an associative processor, and includes a bulk store and monitorsection interrelated to the processor to store filed vehicle plans andcompare each plan as it is filed against all previously filed plans todetermine future potential vehicle conflict and compare all filedvehicle plans against actual vehicle paths to determine future potentialvehicle conflict.
 16. Apparatus according to claim 14 which includes aCRT display scope for a vehicle controller to visually observe thevehicle conflict picture, and means to selectively effect transfer ofinformation from the controller to each vehicle.
 17. Apparatus accordingto claim 14 which includes a trilateration beacon system to determinevehicle position information within the predetermined area, and a backup radar system to obtain vehicle position information for all vehiclesnot responding to beacon, and means to determine weather and terraincharacteristics and effect vehicle control to avoid these.